1. Field of the Invention
The application relates in general to a display device and a method for processing a video signal, and in particular to a display device and a method for processing a video signal which are arranged to determine a source of a video signal by accumulating patterns generated by two adjacent frames.
2. Description of the Related Art
In general, display devices such as LCD monitors, plasma display devices, and video projectors can receive two different types of video signals: video converted from film, and normal video shot by a common digital camera. Video converted from film is composed of frames, whereas normal video is composed of fields, and two adjacent fields form a frame. Furthermore, the playback rates of video converted from film and normal video are also different. In order to play a film which is composed of frames on an average display device, a “PullDown” process must be used to convert the film frames to video frames by separating the film frames into two interlacing fields. As shown in FIG. 1, the film frame A is separated into field A1 and field A2; film frame B is separated into field B1 and field B2; film frame C is separated into field C1 and field C2; film frame D is separated into field D1 and D2; and so on. Hereafter, frame A is copied for generating field A3, frame B is not copied, frame C is copied for generating field C3, frame D is not copied, and so on. Then the video fields A1, A2, A3, B1, B2, C1, C2, C3, D1, D2, . . . , are generated by the cadence of 3:2:3:2. Also, the fields of a video frame can be generated by other cadences, such as a cadence of 3:2:3:2:2, a cadence of 2:2, or a cadence of 6:4. Using the cadence of 3:2 as an example, the first frame is composed of the field A1 and the field A2, the second frame is composed of the field A3 and the field B1, the third frame is composed of the field B2 and the field C1, the fourth frame is composed of the field C2 and the field C3, the fifth frame is composed of the field D1 and the field D2, and so on. This kind of video frame is able to play on the display device which uses the interlaced scanning, because the display device which uses the interlaced scanning will not display two fields of one frame at the same time. However, it will be a problem when this kind of video frame plays on the display device which only supports the progressive scanning. Because the second frame of the video converted from film is composed of the field A3 and the field B1 which come from different scenes, thus they are unable to be combined with each other. Therefore, after receiving the video frame, the type of the video signal must be determined first, such as determining whether the video signal is a normal video signal or a video converted from film. If the video signal is a video converted from film, the cadence of the video frame must also be determined for further processing with a reverse PullDown to make it able to be played correctly on the display device supporting the progressive scanning. In the prior art, for determining the cadence of the video signal, nine frames of the video signal must be read first for obtaining the patterns of 16 bits, then the corresponding patterns are searched in a table for determining the cadence of the video signal. If the patterns cannot be found in the table, the video signal is determined as a normal video signal rather than a video converted from film. However, when the table does not include the types of patterns that correspond to all types of cadence, or an error occurs when obtaining the patterns of the video signal, the type and cadence of the video signal are unable to be determined correctly. Thus, how to easily and correctly determine the type and the cadence of the video signal is a problem which needs to be solved immediately.